The isomerization of β,γ-to α,β-unsaturated steroidal ketones

Steroids and steroidases. IX. Activation parameters and the mechanism of base- and enzyme-catalyzed isomerizations of androst-5-ene-3,17-dione. The nature of the active center of the Δ5 → Δ4-3-ketosteroid isomerase of Pseudomonas testosteroni

“…Analogous mechanism of action studies had not been carried out on the base-catalyzed reaction partly due to the complications of multiple product formation encountered initially (7). However the subsequent delineation of satisfactory conditions for base-mediated isomerizations (4) enabled a mechanistic study of the process to be carried out.…”

Steroids and steroidases. VI. On the C-17 specificity of the Δ5-3-ketoisomerase of Pseudomonas testosteroni and evidence for substrate micelle formation

“…In contrast to the well studied isomerizations of As-3-ketosteroids at low p H (2, 3) few measurements had been made in basic solution presumably owing to the complications arising from multiple product formation (2). That the base-catalyzed reaction was not straightforward (2) was confirmed by the observation that isomerization of androst-5-ene-3,17-dione (la) in a sodium hydroxide solution of pH 9 afforded a mixture containing at least three components.…”

“…Using this t e~h n i q u e ,~ readings could be taken every 8 s. The absorbance of the reaction mixture at infinite time (at least six half-lives) was also determined. The data were then analyzed by the now standard procedure (1)(2)(3).…”

“…The literature reports concerning the C-17 specificity of the A5-3-ketoisomerase of Pseudomonas testosteroni (1)(2)(3), and, in particular, that cholest-5-en-3-one (16) is not a substrate of the enzyme (I), prompted us to investigate systematically the behavior of a series of variously C-17 substituted As-3-ketosteroids towards acid-, base-, and enzyme-catalyzed isomerizations to the corresponding ap-unsaturated ketones. la.…”

Influence of the position of the double bond in steroid substrates on the efficiency of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo steroid Δ4–Δ5-isomerase

“…There are specific difficult, if not impossible, even with the most rapid techniques available, to observe some of the expected intermediate complexes. Therefore, investigations have been undertaken with slower substrates, which have been described previously, but without turnover-number data (Kawahara & Talalay, 1960;Kawahara et al, 1962;Nes et al, 1963). Information about the rate-limiting step involved in the proton-transfer process experiments have been obtained with substrates (3-oxo-A5(10)and -A5(6)steroids) deuterated at a specific carbon position (4ff).…”